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Greetings everyone. It's been a long time since I've checked out this great forum and posted here but I can see all is well within the Guitar Building world.

A couple or three years ago I built a Redwood/Bloodwood Guitar that I've been very very happy with but it's developed a bit of a bulge behind the bridge along with a couple of creases along the bracing.

Here's a couple of pics of the Guitar.






And here's how the top is behaving.






In the last pic I've drawn in the location of the distortions. Creases along the lines and a general bulge behind the bridge.

Here's what the bracing looks like.




If I relax the strings (which I'll do right after posting this the top will come back rather quickly.

I'm usually able to figure out the next step but this one has me stumped. Where should I add a brace(s)? How big? Help.1

Thanks in advance

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Thank You and Best To All

Very bizarre. Looks like my host is not liking the pics I posted. Can't even get into my FTP to check for problems. I'll get it sorted out.

Looks like my host is messed up for now but should be back up shortly. Sorry or any inconvenience.

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Thank You and Best To All

How thick is the top itself?

Thanks for the reply Hupa. I don't know how thick it is and MIGHT have a way to measure it but haven't built guitars in a couple years so tools are quite scattered about.

I'll see if I can find a way to measure it.

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Thank You and Best To All

Here's an idea I came up with. Adding two small braces as shown might strengthen that area where the two braces meet. The extra low profile on the brace that is just behind the bridge plate may not be providing enough strength in that joint area? Thrashing about here so any help appreciated.

Larry

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What is the top thickness?

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Build log

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Thank You and Best To All

Take my suggestion with a grain a salt as I have only built a few guitars, but I am an engineer. I would consider removing the lateral brace under the bridge plate. The lower bout on the guitar wants to bulge when it is under tension. With that lateral brace I suspect instead of bulging across the entire radius of the lower bout the top is folding on the lateral brace. I sort of think pup tent instead of dome.

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http://www.Harvestmoonguitars.com

Top thickness approx. .125 at sound hole.

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Thanks John and very interesting. Had not thought of that. If I do remove that brace there seems precious little left for bracing. Does the idea with additional small braces have any merit from an engineering stand point? It seems as though those two spots are the weak points that are giving way but I'm open to more suggestions.

Remember the guitar is complete at this stage so any work will have be done inside the finished guitar.

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I am not sure, you need more expert advise than mine, but the extra bracing may help if it transfers more of the stress to the xbrace.

In my guitars the xbrace provides nearly all of the real bracing the lower bout.

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http://www.Harvestmoonguitars.com

It doesn't look like excessive belly from the photos.

Doing nothing is the default.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

That follows my thinking but will wait for reinforcements and other opinions.

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Thanks for the look and advice Howard. The challenge I have is it seems to progress over time and it seems to be fairly pronounced in person. Especially the two creases on either side of the bridge. I don't have much experience in these things but would hate to awaken with some genuine damage if it can be stopped now.

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Convert to an adjustable neck , tilt the neck a little forwards and put on a lower bridge/saddle.

Just to cover all bases, how's your humidity?

That bracing scheme does create something like a hinge point just behind the transverse brace so it's not surprising to see it pull up there.

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http://www.chassonguitars.com

Thanks Kent,

Humidity 45% - 55% in San Diego nearly all year with dry 25% for a couple months in the fall but mostly very good.

What would you do to brace or change the bracing to stop it from pulling up there?

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I would leave it go and see if it stabilizes. Guitars develop a bit of belly over time, some faster than others, and most seem to reach a point of equilibrium where all that can move has and it is around that point that they sound their best. It is also true that due to some structural short comings, some guitars do not stabilize resulting in the bridge rolling as the top continues to fail.

I understand a 'wait and see' approach would be difficult for you. But I feel that if you are otherwise happy with this guitar apart from the deformation issue, trying to arrested any 'built in' structural problems by adding or removing wood now is 'very' likely to change more than you would like. As I see it, if indeed this current problem is going to lead to catastrophic failure, there is nothing much you can do to prevent that from happening that is not going impact upon the tone of the instrument in a negative way. So the only real solution to my mind would be to either re-top the guitar now or to wait and see if what you have stabilizes....If it were me, and my guess is that with the top being loaded the way it is this guitar sounds pretty bloody good right now, I would just enjoy playing...even if it is the last dance on the titanic

Cheers

Kim

Thanks Kim,

The guitar is 2 - 3 years old now (maybe more looking at my join date) and it does seem to stop moving at some point but I'm afraid it will go too far one day and re-topping would probably have to be done by someone else as my guitar building days are probably over. It's hard to imagine that adding a couple of little braces would impact the sound that negatively but if it does then turning back would be difficult indeed. Hmm. That's a couple of "don't change anything" words of advice. Any other thoughts?

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Thank You and Best To All

How is the action/tone?

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Old growth, shmold growth!

Maybe it's just the picture but your bridge looks quite thick. What is the distance between the top and the strings in front of the bridge? If it tends to be toward 3/4'', the strings may be too high and exert too much torque on the bridge area, thus exessive deformation (but as Howard mentioned, it may not be exessive after all...).

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Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)

I have doubts that adding some small braces can stiffen it enough to make a difference. If it was mine I would try to wait some more. Some passive intervention is to reduce the action for a bit and switch to lower tension strings. Maybe it will sound even better, who knows, try it.

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Build log

No more difficult to imagine than how the same couple of 'little' braces are going to solve the problem.....if there is one. As I see it its all relative, add a little brace, expect little change, add a big brace, expect big change. Life is so full of compromises...

If you are convinced that this top will fail and remain determine to do a six million dollar man job on it, then I would recommend removing the two finger braces for a start and gluing on new ones aligned more toward 90 degree off the lower legs of the 'X'. How they are set now does nothing at all to direct the longitudinal strength of the grain in the top itself to resist the bridge plate from rolling...



I also feel that the two braces behind that which crosses the rear of bridge plate are too large and too few. I do a similar configuration however I use 3 thin, low, braces on a small top and 5 on an SJ and up..only done a couple with that system but they are hanging in well this far. With redwood, I would use 5.



The same top just over 3 years on shows no deformation, only a nice even dome..




Cheers

Kim

Thanks very much for the post Kim. I wasn't thinking that my next possible step, which was to add two small pieces to the existing bracing to be in the 'six million dollar man' realm but maybe I've mis-posted.

Very interesting to see the fan type bracing and the advice about placing the finger bracing more perpendicular could help matters.

This is my third guitar and haven't built for a couple of years so any internal work at this point seems a but intimidating with removing and replacing braces etc.

Maybe it's not as difficult as it seems?

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The 6 million $ man analogy was in reference to the amount of work that 'I' feel you would need to under take to arrest the problem...if there is one. That is to say that I don't think the two little braces that you plan will do much to help at least in the long term.

It 'is' as difficult as it seems and that is why first advice was to wait and see and if it fails, then re-top because in my opinion and circumstance due to large hands, its just easier that way.